The present disclosure relates generally to imprinting procedures and more particularly to increasing adhesion between elements used in imprinting procedures.
Nano-imprint lithography was initiated as an alternate process to achieve nanoscale features (about 100 nm or smaller) with high throughput and relatively low cost. During the imprinting process, the nanoscale structures are transferred from a mold to a polymer layer. The mold may be used for the thermal imprint process, as well as for the UV-based imprint process.
In the thermal imprint process, to deform the shape of the polymer, the temperature of the film and mold is generally higher than the glass transition temperature of the polymer, so that the polymer flows more easily to conform to the shape of the mold. Hydrostatic pressure may be used to press the mold into the polymer film, thus forming a replica of the mold in the polymer layer. The press is then cooled below the glass transition temperature to “freeze” the polymer and form a more rigid copy of the features in the mold. The mold is then removed from the substrate.
In the alternate UV imprint process, a UV-curable monomer solution is used instead of a thermoplastic polymer. The monomer layer is formed between the mold and the substrate. When exposed to a UV light, the monomer layer is polymerized to form a film with the desired patterns thereon. The UV-based nanoimprint process may generate patterns at room temperature with low pressure.
A potential problem with these techniques is the possible adhesion of the polymer to the mold. If the polymer sticks to the mold, then the imprinted pattern and/or the mold itself may be damaged when pulling the mold off the substrate. This may damage and/or ruin the imprinted patterns and/or deleteriously affect the mold (which may be very expensive and time-consuming to produce).
To reduce the adhesion of the polymer to the mold, high quality releasing self-assembled monolayers (SAMs) have been attached to the surface of the mold by immersing the mold in a solution of the release agent at a concentration of, for example, 1×10−4 M. The improved release properties allowed for the enhancement of pattern resolution in the polymer film. “Release property,” as referred to herein means how well the mold detaches from the polymer layer after imprinting without the polymer sticking to the mold.
However, where the gap between features on the mold is reduced, the problem regarding adhesion of the polymer to the mold may, in some instances, arise even when a releasing layer is disposed on the mold. In those instances, the polymer may stick to the mold gap and detach from the substrate surface. The substrate surface area may not be large enough to hold the resist because the mold surface area facing the resist may be larger.
Thus, there is a need to provide increased adhesion between the polymer and the substrate so as to substantially avoid the foregoing drawbacks.